Capacitor voltage transformers are presently preferred to conventional electromagnetic type transformers because, in comparison, they are less expensive and are smaller in size.
However, due to their construction, CVTs do not have a good frequency characteristic and are generally tuned to give an accurate picture of their primary voltage at a reduced voltage, usually 60 to 110 volts, for the fundamental frequency component only. Accurate measurements at EHV and UHV levels that require a wider bandwidth is not possible if the only instrument transformer present on the system is of the CVT type.
Power quality assessment of electrical power systems has become an important requirement in the modern management of electrical supply systems. One requirement in power quality assessment is compliance with international and domestic standards for harmonic pollution in the system. The standards are applied both to voltages and to currents.
As yet, there is no technically convenient method of measuring harmonic voltages in EHV and UHV systems. This is only possible by using special and costly test and measurement arrangements.